As long as man has gazed skyward and observed birds, he has dreamed of flying. Until comparatively recently, such flight was assumed to be possible only by creating a bird-like structure with flapping wings. The very word ornithopter is derived from the Greek words ornithos meaning bird and pteron meaning wing. In other words, and ornithopter is a device with bird-like, flapping wings.
The concept is not new. The idea of imitating the flights of birds may date back to the Greek legend of Daedalus and Icarus, or perhaps even earlier. However, in approximately 1260, Roger Bacon wrote about the technology of such flight. In the late fifteenth century, Leonardo Da Vinci proposed the concept. Although a workable (i.e., flying) model of his design was, as far as is known, never built, his designs provide the first rigorous, scientific approach to the problem of human, bird-like flight.
Around 1870 in France, Gustav Trouve constructed an ornithopter and managed to fly it approximately 70 meters in a demonstration before the French Academy of Science. Shortly thereafter, Jobert constructed a model of a small bird powered by a rubber band. Many others soon followed with other designs. In the 1890s, Lawrence Hargrave constructed several ornithopters using either steam or compressed air as a power source.
While attention soon turned to fixed-wing aircraft, there were ongoing attempts to create functional, practical ornithopters. Notable among the twentieth century pioneers were Alexander Lippish, Adalbert Schmid and, more recently, James DeLaurier and his team at the University of Toronto.
Ornithopter is a term applied to non-fixed wing aircraft that derives all propulsion from the movement of wings, not from rotors, propellers, or reaction engines. Ornithopters differ in many aspects from fixed-wing aircraft. The greatest difference is that the propelling airfoils utilize reciprocal motion rather than the rotary motion of a propeller or, in the case of helicopters, a rotating wing. The driving airfoils are typically large to interact with a large volume of air, thereby maximizing the generated thrust. The flapping airfoils typically produce both lift and thrust. Consequently, drag-inducing structures common on fixed-wing aircraft may be minimized or eliminated providing theoretically high overall efficiency to ornithopters. Ornithopters do not have control surfaces as commonly used in fixed wing aircraft. Rather, flight control is accomplished by reconfiguring the airframe in a coordinated way, such that the forces active in and on the device produce stable, predictable flight. Possible motions include vertical takeoff and landing, hovering, normal forward flight and gliding.
Ornithopters may be manned or unmanned and range in size from small aircraft models for hobby, recreation, sport and research, and for interacting with wildlife to large, passenger carrying aircraft.
Overall, ornithopters can achieve higher overall efficiency than rotating propeller aircraft. However, the ornithopter body typically rotates counter to the motion of the wing resulting in a motion variously described as heaving, lurching and rising and falling. Such motion has the potential to cause discomfort to passengers carried aboard. It is this single factor, along with the complexity of the required wing and drive mechanisms, that appears to have limited commercial development of the ornithopter as a passenger carrying aircraft.